This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Cognitive deficits in Alzheimer's disease (AD) and related mouse models correlate closely with synaptic deficits. We recently discovered that tau reduction effectively prevents cognitive and synaptic deficits in human amyloid precursor protein (hAPP) transgenic mice, which have high levels of A[unreadable] in the brain and develop several AD-like abnormalities. Because synaptic functions critically depend on the posttranslational modification (PTM) of synaptic proteins, A[unreadable] may alter this process in a tau-dependent manner. To understand AD pathogenesis and how tau reduction prevents AD-like abnormalities, particularly changes of signal transduction pathways at the synaptic junction, synaptosomal and post-synaptic density (PSD) proteins will be prepared from brains of behaviorally tested hAPP/tau+/+, hAPP/tau[unreadable]/[unreadable], tau+/+ and tau[unreadable]/[unreadable]mice. Protein samples will be prepared using sucrose density fractionation and then processed and differentially labeled with isotope-coded labeling reagents. The phosphorylated peptides in the sample will be enriched using metal affinity chromatography, the O-GlcNAcylated peptides in the sample will be enriched using WGA affinity chromatography, and both the PTM-enriched and the PTM-depleted portions of the sample will be further fractionated using other liquid chromatography approaches. The differentially labeled, fractionated samples will be analyzed on the LTQ Orbitrap platform with ETD capabilities and the relative abundance of the different synaptosomal proteins and their PTMs will be compared between the four genotypes. The whole project will be conducted in a collaborative manner using the phospho- and O-GlcNAc-proteomics analysis technical platform developed in the mass spectrometry facility at UCSF.